Rafael Benítez has lamented Chelsea's lack of clinical edge on regular occasions yet he could enjoy one of those days when its presence brought reassurance, together with safe passage, in this FA Cup fourth-round replay.

Brentford were relentlessly game opponents but Chelsea's class stretched them before breaking the visiting team, Juan Mata's fizzing, long-range drive shortly after the interval serving as the prompt for a second-half glut. The scoreline was harsh on Brentford, who were left to lament how close they had come to knocking out the European champions at Griffin Park three weeks ago but Chelsea deserved the reward of a fifth-round trip to Middlesbrough. Their Cup defence is alive and kicking.

Frank Lampard staged his bid for the headlines with the third, arriving late to volley home Mata's cross to bring up his 199th goal in the club's colours. Roman Abramovich, the owner, was present to hear the crowd demand that the midfielder be given the new contract he wants to keep him at Stamford Bridge next season. Inexorably, Lampard is reeling in Bobby Tambling, who has Chelsea's all-time scoring record with 202.

Oscar had flicked in the second and Chelsea's afternoon was completed by the sight of John Terry cavorting in celebration after heading the fourth, from the Brazilian's deep cross. It was only Terry's third start since November, as he has battled the frustration of knee trouble.

For Brentford, there was pride, even if it was tempered by the heaviness of the result. As they had done in the original tie, when Fernando Torres' only goal of the calendar year had bailed out Chelsea, Uwe Rösler's team impressed with the intensity of their pressing and their collective refusal to bow to reputations. But the manager admitted that it was always going to be a struggle to maintain these levels and a mental lapse proved to be the beginning of the end.

The first goal was of tremendous importance, and Brentford thought that they had scored it. The eye-catching Adam Forshaw was fouled on the edge of the Chelsea area by David Luiz in the 39th minute, and the referee Neil Swarbrick whistled immediately for the free-kick, which would come to nothing. Had he waited for a couple of seconds, he would have seen Marcello Trotta ram the ball into the net.

Chelsea, though, did get it and it was nothing short of a disaster for Brentford who, Rösler claimed, had started to make the hosts "run out of ideas.". Mata's finish was magnificent; he took a touch to settle himself before blasting low and left-footed from 25 yards into the bottom corner.

But the build-up had hardly been the product of Chelsea's Premier League quality. Petr Cech hoofed the ball from back to front and Demba Ba won a scruffy aerial challenge to work it to Mata. Simon Moore who, moments earlier, had saved well from Lampard's header, was helpless.

It was a fiercely contested tie, with Rösler noting how Benítez had selected a "physical" team. Some of the challenges overstepped the mark, with Gary Cahill horribly late on Jonathan Douglas in the first-half and David Luiz guilty of a sickening barge on Jake Reeves in the 86th minute, which left the Brentford substitute concussed and his team to play out time with 10 men, Rosler having made all of his changes.

Forshaw was on the right of what was effectively a five-man midfield and Chelsea had to work for space. They came to call the tune although, initially, there was frustration as they spurned a fistful of first-half chances. The best of them fell to Oscar after slick build-up work and a final ball from Mata but, slipping as he shot, the Brazilian hit the outside of the post.

Lampard was in shoot-on-sight mood but his eventual success was presaged by misses. He scuffed from Victor Moses' cut-back – Harlee Dean threw himself in the way of Oscar's follow-up – and volleyed wide when well-placed before half-time. Branislav Ivanovic had threatened with a header for Chelsea while Forshaw twice went close from distance at the other end.

After Mata's breakthrough the pain arrived for Brentford. The substitute Eden Hazard fed the overlapping Ivanovic, after Toumani Diagouraga's loose pass and Oscar's deflected back-heel wriggled underneath Moore and beat Dean on the line. Then came Lampard and Terry, the old one-two, for numbers three and four. For Benítez, there was beauty in the routine.